1. Field
The present invention relates generally to electronics, and more specifically, to zero tracking for low drop output regulators.
2. Background
Power management circuits often employ low drop output (LDO) regulators. A LDO regulator is capable of supplying a programmable voltage to a complex system of circuits from a single source, such as a battery. In order to limit undershoot of the output during current load transitions, a large bypass capacitor is often placed at the output of the LDO regulator. This capacitor also tends to stabilize the LDO regulator by adding a dominant pole at the output. As long as the dominant pole is sufficiently far from the other poles to achieve a 45° phase margin, stability is maintained.
Many applications today, such as cellular telephones and the like, require high performance LDO regulators. At the same time, manufacturers and designers are continuously attempting to provide a more compact solution that is lower in cost, more reliable, and consumes less power. A smaller bypass capacitor which could be integrated into the LDO regulator would serve these objectives well. The problem faced by designers is that the frequency of the dominant pole is set by this capacitor. As the capacitor value is decreased, the frequency of the dominant pole is increased. As the dominant poles moves towards the frequency of the other poles in the LDO regulator, the phase margin is reduced. At some point, the LDO regulator no longer has a dominant pole at the output, and behaves as a second order system. As a result, it becomes increasingly more difficult to maintain the stability of the LDO regulator under all current load conditions. Accordingly, there is a need for an innovative approach to ensure the stability of the LDO regulator under any current load variations with smaller capacitor values than are currently employed today.